The present invention relates generally to biosynthetic processes and more specifically to organisms capable of using carbohydrates, methanol, synthesis gas and other gaseous carbon sources in the production of commodity chemicals.
1,3-butanediol (1,3-BDO) is a four carbon diol traditionally produced from acetylene via its hydration. The resulting acetaldehyde is then converted to 3-hydroxybutyraldehdye which is subsequently reduced to form 1,3-BDO. In more recent years, acetylene has been replaced by the less expensive ethylene as a source of acetaldehyde. 1,3-BDO is commonly used as an organic solvent for food flavoring agents. It is also used as a co-monomer for polyurethane and polyester resins and is widely employed as a hypoglycaemic agent. Optically active 1,3-BDO is a useful starting material for the synthesis of biologically active compounds and liquid crystals. Another use of 1,3-butanediol is that its dehydration affords 1,3-butadiene (Ichikawa et al., J. Molecular Catalysis A-Chemical, 231:181-189 (2005); Ichikawa et al., J. Molecular Catalysis A-Chemical, 256:106-112 (2006)), a chemical used to manufacture synthetic rubbers (e.g. tires), latex, and resins.
Synthesis gas (syngas) is a mixture of primarily H2 and CO that can be obtained via gasification of any organic feedstock, such as coal, coal oil, natural gas, biomass, or waste organic matter. Numerous gasification processes have been developed, and most designs are based on partial oxidation, where limiting oxygen avoids full combustion, of organic materials at high temperatures (500-1500° C.) to provide syngas as a 0.5:1-3:1 H2/CO mixture. Steam is sometimes added to increase the hydrogen content, typically with increased CO2 production through the water gas shift reaction. Methanol is most commonly produced industrially from the syngas components, CO, and H2, via catalysis.
Today, coal is the main substrate used for industrial production of syngas, which is traditionally used for heating and power and as a feedstock for Fischer-Tropsch synthesis of methanol and liquid hydrocarbons. Many large chemical and energy companies employ coal gasification processes on large scale and there is experience in the industry using this technology.
Moreover, technology now exists for cost-effective production of syngas from a plethora of other materials such as biomass, wastes, polymers, and the like, at virtually any location in the world. The benefits of using syngas include flexibility, since syngas can be produced from most organic substances, including biomass. Another benefit is that syngas is inexpensive. In addition, there are known pathways, as in organisms such as Clostridium spp., that utilize syngas effectively.
Despite the availability of organisms that utilize syngas, in general the known organisms are poorly characterized and are not well suited for commercial development. For example, Clostridium and related bacteria are strict anaerobes that are intolerant to high concentrations of certain products such as butanol, thus limiting titers and commercialization potential. The Clostridia also produce multiple products, which presents separations issues in obtaining a desired product. Finally development of facile genetic tools to manipulate Clostridial genes is in its infancy; therefore, they are not readily amenable to genetic engineering to improve yield or production characteristics of a desired product.
Increasing the flexibility of inexpensive and readily available feedstocks while minimizing the environmental impact of chemical production are two goals of a sustainable chemical industry. Feedstock flexibility relies on the introduction of methods that enable access and use of a wide range of materials as primary feedstocks for chemical manufacturing. The reliance on petroleum based feedstocks for either acetylene or ethylene warrants the development of a renewable feedstock based route to 1,3-butanediol and to butadiene.
Thus, there exists a need to develop microorganisms and methods of their use to utilize carbohydrates, methanol, syngas or other gaseous carbon sources for the production of 1,3-butanediol. The present invention satisfies this need and provides related advantages as well.